This invention relates to an improved intraocular lens for implantation in the eye following removal of the natural lens during cataract surgery. More specifically, it relates to such an intraocular lens with at least one filamentary support member, or "haptic", which exhibits an increased resistance to breakage during manipulation.
The filamentary haptic of an intraocular lens is designed to facilitate insertion of the lens into the eye and to provide stable fixation of the implanted lens to prevent the lens from decentering. The filamentary haptic is attached to and extends outwardly from the periphery of the optical lens body. Most intraocular lenses have two haptics displayed at positions 180.degree. apart from each other on the optical lens body.
It is critical that the haptic of the lens exhibits adequate resiliency and significant resistance to breakage during use. Although certain haptic materials such as polypropylene offer acceptable resistance to breakage, other conventionally used haptic materials such as polymethylmethacrylate (PMMA) are brittle and are frequently prone to breakage. This problem becomes especially acute when the haptics are lathe cut from a single lens blank to prepare a one-piece lens with integrally attached haptics. The problem of haptic breakage is a serious one, and efforts have been made to provide the haptics with an increased resistance to breakage.
One such effort is disclosed in U.S. Pat. No. 5,037,435. The '435 patent describes preparing intraocular lenses with haptics exhibiting high fracture toughness. The haptics are composed of a polymer matrix with from 0.1 to 0.5 percent by weight of dispersed, solid particles of an inorganic, biocompatible material. The inorganic materials disclosed include titanium dioxide, fumed silica, barium sulfate and copper phthalocyanate. Organic, elastomeric materials such as polybutadiene are also described. Unfortunately, the haptics of these intraocular lenses fail to exhibit significantly increased fracture toughness because the particle concentration in the matrix is too low to have any beneficial impact, and the inorganic materials disclosed do not impart desired toughness properties regardless of concentration. In addition, the incompatibility of conventional elastomeric materials, such as polybutadiene, with a rigid polymer matrix such as PMMA, prevents increasing the concentration of conventional elastomeric particles to an amount necessary to improve breakage resistance without diminishing the physical and mechanical properties of the rigid polymer matrix.
In view of the deficiencies of the prior art, it would be desirable to fabricate an improved intraocular lens with filamentary support haptics that exhibit an enhanced ability to withstand breakage during routine handling.